This invention relates to the preparation of Diels-Alder dienophile diadducts of gamma-terpinene, and more specifically, to the high yield preparation of maleic anhydride diadducts of gamma-terpinene.
It is well known that Diels-Alder dienophile monoadducts of terpenes, which are here defined as molecules which result upon covalent joining of one molecule of a Diels-Alder dienophile and one molecule of a terpene, can form upon contact of Diels-Alder dienophiles and terpenes at elevated temperatures. Minor amounts of diadducts, which are here defined as molecules in which there is a covalent joining between two molecules of a Diels-Alder dienophile and one molecule of terpene, can also form upon contact of Diels-Alder dienophiles and terpenes at elevated temperatures. For example, U.S. Pat. No. 1,993,031, issued to Peterson, discloses that an amorphous resinous compound may be produced by reacting maleic anhydride, a typical Diels-Alder dienophile, with a terpene cut comprising terpenes having a non-conjugated system of double bonds. Such terpenes are disclosed as being alpha-pinene, beta-pinene, terpinolene, and d-, 1- and d,l-limonene. All of these terpene isomers are readily available by the distillation of turpentine or orange oil, and it is now known in the art that their reaction with maleic anhydride gives a product in which the major component is monoadduct. Gamma-terpinene comprises a minimal portion of turpentine and is not cited in the bulk of this literature.
Despite a wealth of literature relating to the reactions between terpenes and maleic anhydride, there has long been a need for a process by which substantial yields of maleic anhydride diadducts of terpenes could be obtained. High yield methods for preparing such diadducts are especially desirable, since the process of separating undesirable monoadducts from diadducts is costly and time-consuming. In an attempt to provide such a process, Schluenz et al, in U.S. Pat. No. 4,107,420, proposed reacting a non-conjugated terpene and maleic anhydride, preferably in equimolar amounts, at temperatures between 140.degree. C. and 200.degree. C. in the presence of 0.002 to 0.03% iodine, based on the weight of the terpene. Schluenz et al claimed that by using this process they could prepare a mixture containing more than 15% diadducts; their examples show the preparation of reaction products containing up to 45% diadduct. Terpenes disclosed as being useful in the Schluenz et al process include limonene, terpinolene, terpineol, 1,8-cineole, 1,4-cineole, and gamma-terpinene (1,4-para-menthadiene). However, gamma-terpinene is not actually utilized in any of the provided examples. Nor do they claim their process produces a specific diadduct, for example, the diadduct of gamma-terpinene. Rather their process produces a complex mixture of isomeric diadducts.
Although Schluenz et al disclose and claim the use of iodine in their process, Example 4 in their patent illustrates the process run in the absence of iodine using terpinolene as the terpene. The resulting reaction product comprises about 45% of diadduct, a yield essentially the same as that obtained in the presence of iodine. However, the product obtained in the absence of iodine is dark yellow in color rather than pale yellow. The Schluenz process, then, apparently improves the color of the product but not the yield of diadduct.
U.S. Pat. No. 4,670,504 to Cardenas discloses a tackifier composition formed from a resin which is preferably a polymerized terpene that subsequent to formation is reacted with an acid or anhydride such as maleic anhydride. It is disclosed that gamma-terpinene is one of many possible terpenes which can be used to prepare the polyterpene. The anhydride is said to become chemically incorporated with the polyterpene in a manner which does not appear to be fully understood. The addition of maleic anhydride to a pre-existing terpene polymer is to be distinguished from the present invention in which maleic anhydride is added to terpene monomer.
Diels-Alder dienophile diadducts of gamma-terpinene are expected to find extensive commerical use. For example, maleic anhydride diadducts will likely be employed in alkyd formulations and as curing agents for epoxies and the like. Adduction between maleimides or bismaleimides and gamma-terpinene may lead to novel polyimides and/or their precursors. The product polyimides are expected to be useful composite components for high temperature structural applications. So called "mixed" Diels-Alder dienophile diadducts of gamma-terpinene, in which one molecule of gamma-terpinene is covalently joined with one mole each of two different Diels-Alder dienophiles, such as maleic anhydride and acrylic acid, are expected to be useful as well.
Therefore, it is an object of this invention to provide diadducts of gamma-terpinene and maleic anhydride, maleimides, and acrylates, respectively.
It is another object of this invention to provide "mixed" diadducts of gamma-terpinene.
It is a further object of this invention to provide diadducts of gamma-terpinene and various Diels-Alder dienophiles.
It is still another object of this invention to provide diadducts of gamma-terpinene and various Diels-Alder dienophiles without appreciable formation of monoadducts.
It is yet another object of this invention to provide diadducts of gamma-terpinene and various Diels-Alder dienophiles in a more economically desirable manner than previously known methods.